CVE-2016-20021 in Portage
Summary
by MITRE • 01/12/2024
In Gentoo Portage before 3.0.47, there is missing PGP validation of executed code: the standalone emerge-webrsync downloads a .gpgsig file but does not perform signature verification.
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Analysis
by VulDB Data Team • 02/02/2024
The vulnerability identified as CVE-2016-20021 affects Gentoo Portage versions prior to 3.0.47, specifically targeting the emerge-webrsync utility which is responsible for downloading and synchronizing package repositories from remote sources. This flaw represents a critical security weakness in the package management ecosystem where the system downloads cryptographic signatures but fails to validate them, creating a potential attack vector for malicious code injection. The issue stems from the absence of proper PGP signature verification during the webrsync process, which is designed to fetch package metadata and repository information from trusted sources.
The technical implementation flaw occurs within the emerge-webrsync utility's handling of GPG signatures where the system correctly downloads the .gpgsig files containing cryptographic signatures but subsequently ignores the verification process. This creates a scenario where an attacker could potentially compromise the package repository by replacing legitimate signature files with malicious ones, while the system continues to operate under the assumption that all downloaded content is authentic. The vulnerability directly relates to CWE-310, which addresses cryptographic weaknesses in signature verification mechanisms, and represents a failure in the principle of least privilege where the system accepts potentially compromised code without proper authentication checks.
The operational impact of this vulnerability extends beyond simple package management, as it compromises the integrity of the entire Gentoo package ecosystem. Attackers could exploit this weakness to inject malicious code into package repositories, potentially affecting thousands of systems that rely on Portage for package management. The consequences include potential system compromise, data exfiltration, and the ability to establish persistent backdoors through compromised package installations. This vulnerability particularly affects systems that depend on automated repository synchronization and could enable sophisticated supply chain attacks where legitimate package repositories are poisoned with malicious content.
Mitigation strategies for CVE-2016-20021 require immediate upgrade to Portage version 3.0.47 or later where proper PGP signature validation has been implemented. System administrators should also implement additional security controls such as verifying package integrity through multiple independent sources and maintaining offline backup repositories with verified signatures. Organizations should consider implementing network monitoring to detect unusual download patterns and establish robust incident response procedures for signature verification failures. The remediation process must include comprehensive testing of the updated system to ensure that PGP validation functions correctly and that all package repositories are properly authenticated before any synchronization occurs. This vulnerability highlights the critical importance of cryptographic verification in package management systems and aligns with ATT&CK technique T1195 which addresses supply chain compromise through package repositories.